Cement is employed in compositions to form concrete, grouting and mortar, which compositions also contain other components such as sand, gravel or stone. Although there are several classes of hydraulic cements, eg. gypsum, high alumina cements and Portland cement, the latter is the most commonly used in structural applications and is high in silica content. In this disclosure the term "cement" shall refer to silicate cement compositions including Portland cement, pozzolanic cements, hydraulic limes, fly ash and natural cements.
Cement compositions are rendered useful by combining its solid components with water. An amount of water in excess of that required for hydration is necessary to obtain a mixture with sufficient workability, i.e. gives a mixture which flows readily for pouring into a form or mold of the desired structure. During the hardening process, the excess water remains and, as it evaporates, causes cavities to be formed in the molded structure. These cavities reduce the integrity of the structure and result in a lower compressive strength than is theoretically attainable. It, therefore, is desirable to use the lowest amount of water possible with the composition in order to obtain the best compressive strength. Low amounts of water, however, make workability difficult so that a compromise must be made.
Additives which cause the strengthening of cement mixtures while allowing adequate workability are commonly referred to as water reducers or plasticizers. Additives which allow very low water levels are called superplasticizers. When used in mixtures containing normal levels of water, the result in a mixture having increased fluidity and workability. Commonly used commercially available compounds useful as superplasticizers include sulfonated melamine-formaldehyde condensates, sulfonated naphthalene-formaldehyde condensates, sulfonated polystyrenes and sulfonated styrene/maleic anhydride copolymers as well as other sulfonated copolymers of styrene. Naphthalene-formaldehyde sulfonates and salts of sulfonated styrene-indene copolymers are taught as fluidizing agents in U.S. Pat. Nos. 4,164,426 and 4,071,493, respectively. Sulfonated polymers and copolymers of styrene are taught in British Patent No. 1,588,130 and U.S. Pat. No. 4,076,699, respectively.
The present invention provides new compositions comprising polymers and copolymers of hydroxyalkyl (meth)acrylates as fluidizing agents for cement mixtures.